Promotional Catalytic Activity of Bifunctional Ru-Ce-Zr Catalysts forNH3-SCO by Deposition Order of Dual Active Components

The ammonia fuel injected into the combustion chamber cannot be completely combusted resulting in high levels of escaped ammonia in the ammonia-fueled engine exhaust. It is a feasible way to obtain ammonia selective catalytic oxidation (NH3-SCO) catalysts with excellent performance using noble metal-transition metal catalysts. In this work, a series of Ru-Ce-Zr bifunctional catalysts were synthesized by precipitation and impregnation methods to investigate the influence of introduction methods of different active components (Ru and Ce) on their physicochemical properties and NH3-SCO performance. Among them, the BET and NH3-TPD results showed that Ru-Ce/ZrO2 (RC/Z) catalyst had the largest specific surface area and NH3 desorption amount, indicating that its surface could capture more NH3. More importantly, compared to other catalysts, RC/Z catalyst exhibited highest relative concentration of Ce3+, which facilitated electron transfer via Ce4+ + Ru3+ ↔ Ce3+ + Ru4+. The Ru-Ce/ZrO2 catalyst exhibited the best catalytic performance under the strong interaction between Ru and Ce species. its NH3 conversion reached 100% and N2 selectivity was 95.7% at 237 °C. The N2 selectivity exceeded 70% over a wide temperature range of 150–400 °C. In situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) showed that the surface of RC/Z catalyst exhibited the highest amount of Lewis and Brønsted acid sites, which might be one of the reasons for its excellent N2 selectivity. This work revealed the effect of the way of introduction of Ru and Ce active species on their NH3-SCO performance.